When making an external call, Presentation Number is the number that is displayed on the called persons phone. (If they have a suitable service and phone: e.g. Caller Display at home, or a mobile)

Before the migration to the current CallManager VoIP phone system, the University's phone system was unable to transmit any presentation number informaion, so all calls appeared to come from (01223) 336633. If someone called 01223 336633, they just got a message saying that someone from the University tried to call them, but we could not say who. The new CallManager system can transmit correct presentation number

The procedures and options detailed here have no impact on the name or number displayed when making internal calls.

It is not possible to specify per call, which presentation number (main or DDI) is sent.

Presentation number has now been activated for most institutions. The institutions listed at the bottom of this page have opted out of presentation number, and will always transmit 01223 336633 regardless of what is set in Admin.Phone or My.Phone.

DDI. The extension's full DDI number is transmitted as the presentation number.

Main. 01223 336633 is transmitted as the presentation number.

Institution. (Not currently available in My.phone). This is a pre-selected number, configurable in admin.phone.cam.ac.uk under the "Institution Details" menu.

Other. (Only available in admin.phone) Here you can select any other phone number in your institution to be set.

The default in Admin.phone is that all extensions are set to DDI.

See below for details regarding extensions whose number start with "16"

When Presentation Number is transmitted.

The University has multiple links to the public (& private) telephone network. These links all handle presentation number in different ways.

O2. The O2 links are used for all Mobex traffic (5xxxx numbers). The plain 5-digit extension is always transmitted down this link. (The DDI option in Admin.phone has no effect on this.)

BT. This is used for calls to numbers beginning 08 (e.g. 0800, 0845). If the selected presentation number begins "01223 33" then the number will get transmitted down this link. Any other number (e.g. 01223 74xxxx or 01223 76xxxx) will get changed to 01223 336633. This is a restriction by BT, and there is nothing the University can do to get this changed.

Virgin. This is used for all other traffic. Whatever is selected in Admin.phone is transmitted down this link.

It is not possible to manually route a call down a particular link. The phone system chooses what it considers the best link at the time.

Ex-Directory/16xxx Extension Numbers

Some people have extension numbers starting "16". These numbers are uncallable from anywhere. Even though they may be displayed via the Vodafone & private links, it will not be possible for anyone to return these calls. Institutions must ensure that either these extensions are set in Admin.phone to "Main", or that they contact the Telecomms Helpdesk and ask for another (valid) University number to be presented.

Opted Out Institutions

The following institutions have opted out of presentation number and will always send out 01223 336633. If the institution wishes to change its mind, we require an email from your Telephone Liaison Officer.